1. Field of the Invention
The present invention relates to a machine for folding and peripheral glueing of the edges of sheet material and the like.
In particular the present invention relates to a machine for folding and glueing of the upper in the manufacture of a shoe or leather products.
The invention also relates to a method for definition of the operating parameters in a machine for folding and peripheral glueing of the edges of sheet material and in particular for folding and glueing of the upper in the manufacture of a shoe or leather products.
For the sake of simplicity the present invention is described below in relation to the manufacture of shoes, however the invention finds application in the production of various types of products which require folding and glueing of sheet materials such as belts, wallets, purses and the like. The machine of the present invention can be used for these applications merely by replacing appropriate tools. The present description is therefore not intended to be limiting but extends also to machines for the fabrication of these products.
Description of the Prior Art
Machines of this type, also known as gluer-folders, comprise a working top on which is made to travel the piece to be folded peripherally and a main shaft driven through a transmission by an electric motor.
The main shaft drives various members for the transport with reciprocating movement of the work to be processed in accordance with straight or curved directions and for movement lengths (so-called movement pitch) varying in accordance with the length to be executed. The pitch movements take place thanks to a second motor, generally of the step or some other type.
Folding means are also provided for folding the work piece peripherally, pressing means for holding and advancing the folded piece, a glue feeder, and a plurality of photoelectric cells located in various points of the work top to identify the presence and serial conformations of the work piece being processed. The signals detected by the photoelectric cells allow automatic control through processing circuits of the beginning and end of application of the glue, reduction or increase of the pitch in accordance with the type of length (of folding) to be executed, main motor speed change, insertion of a cutting blade, etc.
Means for folding of the length to be folded generally consist of a folding shoe cooperating with a guide or fixed striker and an oscillating finger for folding the edge of the piece against the folding shoe.
Usually the folding shoe is axially hollow and through it is fed the glue in a predetermined quantity depending on the machine rotation speed and pitch. The glue is kept at a predetermined temperature in a tank and delivered through a gear pump controlled through servomechanisms by an electric motor, e.g. a step motor.
There are also provided knives or blades for performance of cuts in the work piece to facilitate folding generally opposite the internal curvatures.
These machines were originally provided for use substantially under manual control and were recently equipped with automatic control means of the electronic type based on programmed microprocessors in which the working parameters can be modified in accordance with the work piece being processed, thus providing automatic operation but still under the supervision of the operator.
Typical operating parameters in this sense are speed of feed, transport pitch, glue delivery, etc.
It has also been proposed to equip the control unit with a sufficiently capacious memory to contain the functional parameters of a large number of work pieces which the machine is capable of producing. These parameters are memorized in advance and in fact constitute an essential part of the machine. The parameters of a given piece are called up upon selection by the operator of this piece which, for example, is characterized by the type of shoe, the number, right or left, type of leather, etc. A machine of this kind is described for example in EP-A-0 340 695.
Folding-glueing machines of the above type have however some limitations and shortcomings.
In the first place, for these known machines it is necessary to define in advance all the parameters of the several uppers or in general of the pieces to be processed and memorize them. Therefor this machine has considerable complexity of the setting up operations and in addition is preset for a certain number of uppers or pieces which may never be used during the life of the machine.
In addition, programming of the parameters can be excessively rigid, e.g. a lot of skins softer than foreseen can require reprogramming at least of some parameters of a setting, which is performed on the basis of defects found in the first pieces processed.
Finally, known machines allow memorization only of three values for each of the main parameters of speed and pitch, i.e. one for the straight lengths, one for the curved lengths with inward concavity (internal curves), and one for the curved sections with outward concavity (external curves).